Andrew Flintoff may not be fit for the fourh Ashes Test, which begins at Headingley on Friday. Photograph: Darren Staples/Reuters

At what point does one of the most inspirational figures in England's cricketing history become a liability? That player in question, naturally enough, is Andrew Flintoff and the outcome of the Ashes series could hinge on England making the correct decision over the next few days as to whether he should play in the Headingley Test. The greatest gamble of the Ashes summer is upon us.

Flintoff sought more advice, perhaps even comfort, back in Lancashire today from his physiotherapist, friend and confidant Dave Roberts, with the possibility of a third cortisone injection in less than a fortnight high on the agenda to try to help him through this Ashes series that he is desperate to complete. That would be the sixth injection of the summer. He will have a constant reminder of his Ashes heroics in old age.

According to England's coach, Andy Flower, Flintoff is "bullish" about his chances of playing in the fourth Test, which begins in Leeds on Friday. "He is confident that he will play," said Flower. "He is a strong bloke, a strong body and a strong will and he wants to play these last two Test matches. If he is fit, enough he will play."

Nevertheless Flower, like everybody, witnessed Flintoff's limping finale at Edgbaston on Monday and, given the chance to dismiss as mind games the assessment of Australia's captain, Ricky Ponting, that Flintoff was "going downhill quickly", he did nothing of the sort. "I suppose continued wear and tear would mean that the percentages would say he is less likely to play. But he will have a good idea of how his body feels. We have played it by ear throughout the series and we will have to do that again leading up to Headingley."

If Flintoff cannot raise a gallop then indications are that England will settle for a Trott: Jonathan Trott. Warwickshire's South African-born batsman, who is averaging 99.75 in championship cricket, heavily assisted by Edgbaston's moribund pitches, would then almost certainly make his Test debut at No6, as an additional specialist batsman, with Flower having stressed that Ravi Bopara is safe at No3.

However much England's chief selector, Geoff Miller, suggests options in a 14-strong squad are numerous, the likelihood of England batting Stuart Broad as high as No7 at Headingley with a 1-0 lead in the series to protect and unsettled weather about is negligible. Broad's place would be under threat if England opted for only four bowlers, either from Steve Harmison, who would be an obvious bowling replacement for Flintoff as an impact bowler but is afflicted by blisters, or by the left-arm swing of Ryan Sidebottom.

Sidebottom has recovered something approaching his best form recently, now has 27 first-class wickets at 23 runs each at Nottinghamshire, and could fulfil a stock-bowling role on a Headingley pitch he grew up on. Even if Flintoff is passed fit, it will still be with reservations about his bowling, which might mean Sidebottom edges out Broad or even Graeme Swann for the final bowling place.

If Broad is omitted, he would go down with some praise from his coach. "He has handled everything that international cricket has thrown at him incredibly well since he came in,'' Flower said. "I think he is a fantastic young cricketer now and he is going to be even better as he progresses and as the team progresses.

"I am very happy with Stuart, he is a great competitor who is learning about bowling and batting in the best arena possible and he is doing very well. His innings at Edgbaston was impressive and the last time we played at Headingley he played an even more impressive knock against the South Africans. That is a factor that will be taken into account but once we know the fitness situation we will try to balance the side as best as possible.''

Australia also have fitness concerns, with Michael Clarke, who made an unbeaten century at Edgbaston, undergoing treatment for an abdominal strain.